The present invention relates to a transmission mechanism for transforming a continuous rotating motion into an intermittent rotating motion, which comprises a rotating disk-crank and a kinematic chain that links said disk-crank with an output shaft with the cooperation of cam means; and it also relates to a device for transporting sheets of laminar material which is provided with such a transmission mechanism.
Some machines for working sheets of laminar material, such as presses for cutting, cutting out, die-cutting, scoring and/or embossing sheet materials such as paper, cardboard, wood, plastics and the like require the sheets of material to be transported along a path in an intermittent manner, so as to carry out a number of operations on them.
For this purpose, the machines have transporting devices for such sheets which consist in transversal bars of clamps regularly spaced along endless chains. The chains are driven with an intermittent motion, so that the bars are drawn intermittently.
A transporting device of this type is described in patent ES 482310 from the Applicant. In that device, the constant-speed rotation of an organ of the machine is transformed into an intermittent rotation of the shaft driving the chains by means of a transmission mechanism which includes a toothed segment.
This transmission mechanism is satisfactory in general, but it has the disadvantage of requiring a considerable amount of assembly, adjustment and set-up work. Furthermore, for some applications it is excessively bulky.
The aim of the present invention is to solve the mentioned drawbacks by developing a transmission mechanism that does not require complicated adjustment and setting up and that has a low execution cost.
In accordance with this aim, the mechanism of the present invention is characterised in that said kinematic chain includes a lever mounted so as to rotate freely on a shaft fixed in an eccentric position of said disk-crank, and in that said lever is guided in its movement by said cam means and acts upon a driving arm which is attached for joint rotation to the output shaft.
The lever and arm system which replaces the toothed sector of the prior art reduces the cost of the mechanism both in terms of its execution and due to the fact that setting up is eliminated.
In one embodiment, the lever acts upon the driving arm through a connecting rod which is hinged on one side to a shaft fixed onto the lever and on the other side to an eccentric shaft of the driving arm.
Preferably, the aforesaid cam means include a fixed cam, while the lever has a shaft fixed thereto and provided with bearing elements, which is coupled to the fixed cam.
In one particularly advantageous embodiment of the invention, the aforesaid disk-crank is driven from a second disk-crank by means of a connecting rod hinged between two eccentric shafts of the two disk-cranks, said second disk-crank being mounted so as to rotate around a shaft which is offset with respect to the rotating shaft of the first disk-crank.
The presence of two disks having different centres produces an oscillating movement within the cycle, which means that large level differences or jumps in the cam means can be avoided, thereby reducing the overall size of the mechanism and the magnitude of stresses.
In accordance with one embodiment, the second disk-crank is driven in rotation through a safety clutch.
In accordance with one particular method of construction, the first disk-crank is mounted so as to rotate freely on the output shaft itself. The size of the mechanism is reduced thereby.
In another aspect, the invention relates to a device for transporting sheets of laminar material which is provided with a transmission mechanism such as that described.
Advantageously, the transporting device is such that the output shaft has drawing wheels mounted on it for drawing chains with transporting bars provided with clamps for gripping the sheets to be transported.